1) Field of the Invention
The present invention relates to seats, both those intended to be static, such as chairs, armchairs or stools, and those to be fitted to vehicles. It concerns, more particularly, both an ergonomic seating module and a chair fitted with said module.
2) Description of Related Art
It should be understood that, for the purpose of simplification, the expression “seating module” will be sometimes replaced, in this document, by the word “seat”, designating the part of the chair forming the actual seat on which the buttocks are placed.
In static chairs, the seat is generally formed of a plate made of rigid material, which may be covered with a cushion. This seat may be completed by a back and by armrests. Certain chairs, more particularly intended for persons working in offices, for example, with a computer, include joints and elastic members for inclining more or less the seat and the back. Despite all the improvements made, health problems, especially relating to the vertebral column, continue to exist, causing great injury to those who suffer therefrom and resulting in significant absenteeism, which is detrimental to businesses.
Bicycle or moped saddles, for example, generally include a rigid frame, including a pommel element and a cantle element, and a part, generally of triangular shape connecting the pommel element to the cantle element and forming the support surface. This part has a certain flexibility allowing adaptation to the position of the user, defined by adjusting various parts of the vehicle. Saddles of this type have been arranged on fixed supports, in order to make static chairs. If, in general, the comfort of a bicycle saddle is not disputed, the application of the same principle to a fixed chair is unconvincing. This is probably due to the fact that, in a static situation, the user's limbs, in contact with the seat, remain fixed, whereas on a bicycle, they are in almost permanent movement.
In order to properly understand the problem of chairs, it is helpful to recall the use that is made thereof. Today, the seated position has become one of the most representative of professional activity. Within this scope, two sorts of quite distinct attitude generally occur, depending upon whether the occupation is “active” or “passive”. An “active” occupation means one in which the hands are used a great deal, for example for typing on a keyboard, drawing, any seated manual work (watchmaking, electronics, laboratory, clothing industry, . . . ) or driving a vehicle. The body thus has to be placed such that the hands can carry out their function. It is generally positioned with the trunk oriented substantially vertically. Conversely, in “passive” occupations, such as discussions, moments of reflection or relaxation, the hands are much less used and the body can be placed such that the back is resting against a backrest, the trunk inclined backwards.
Designers of chairs for seated work make them so as to prevent any stress on the musculature. If this approach is proper during phases of “passive” occupation, which allow the body to rest, it is detrimental to the organism in phases of “active” occupation. Indeed, it appears that what, at the start, is perceived as additional comfort, leads to a weakening of the supporting muscles, which can cause numerous annoyances, lumbar pains being the most frequent.
Experience seems to show that the health problems, encountered by people working in a seated position, could arise from a weakening of the supporting musculature. This musculature does not directly participate in the person's mobility, but allows him to ensure a position of balance, both when the person is standing, stopped or moving, and when the person is sitting or squatting. It can only develop or be maintained harmoniously if it is regularly used, while preventing crispation of one muscle or another.
It is an object of the present invention to provide a chair fitted with an ergonomic seat which practically forces the user to adopt a posture in which his supporting musculature is used naturally and automatically, thus preventing health problems.
More specifically, the invention concerns a seating module, which includes:                a structural framework provided with a pommel element,        a frame provided with a cantle element, said structural framework and said frame having planar symmetry,        means for connecting the structural framework to the frame, including a joint which allows the frame to tilt, in relation to the structural framework, about an axis perpendicular to the plane of symmetry, and        a seat connecting the frame to the pommel element and formed of an elastic membrane whose function is to define a rest position of the frame in relation to the structural framework and to return it to this position when a user tilts it in one direction or another.        
The seating module according to the invention further includes the following main features:                in the rest position, the frame is inclined forwards by an angle of approximately 10° in relation to the ground;        the structural framework has, in plane, a T-shape, the vertical bar of which, arranged in the plane of symmetry, extends forwards and is bent upwards to end in the pommel element;        the ends of the horizontal bars of the T are raised to form the joint with the structural framework;        the frame is a fork which, in plane, has a U-shape with an axis disposed in the plane of symmetry, the cross bar of which is raised and forms the cantle element and the two vertical bars of which extend forwards, substantially as far as the pommel element, which is underneath it;        the membrane forms a support surface that is convex along a line perpendicular to the plane of symmetry and concave along a line inscribed in this plane;        the membrane is fixed between the pommel element and the cantle element, between the two teeth of the fork, and between the ends of the teeth and the pommel element;        the membrane is covered by a padding member forming a cushion and includes a longitudinal groove intended to form a space for receiving the user's coccyx.        
The present invention also concerns a chair provided with a support in contact with the ground and a seating module as defined hereinbefore, characterized in that the support includes an arm extending forwards and upwards and carrying a cross bar forming a support for the user's knees and padded to form a cushion.